package com.hzlh.utils;

import java.io.*;

public class Base64Decoder extends FilterInputStream {

	private static final char[] chars = {  
		 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',  
		 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',  
		 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd',  
		 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',  
		 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x',  
		 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7',  
		 '8', '9', '+', '/'  
		};  
		  
		// A mapping between char values and six-bit integers  
		private static final int[] ints = new int[128];  
		static {  
		 for (int i = 0; i < 64; i++) {  
		   ints[chars[i]] = i;  
		 }  
		}  
		  
		private int charCount;  
		private int carryOver;  
		  
		/*** 
		* Constructs a new Base64 decoder that reads input from the given 
		* InputStream. 
		* 
		* @param in the input stream 
		*/  
		public Base64Decoder(InputStream in) {
		 super(in);  
		}  
		  
		/*** 
		* Returns the next decoded character from the stream, or -1 if 
		* end of stream was reached. 
		* 
		* @return  the decoded character, or -1 if the end of the 
		*      input stream is reached 
		* @exception IOException if an I/O error occurs
		*/  
		public int read() throws IOException {
		 // Read the next non-whitespace character  
		 int x;  
		 do {  
		   x = in.read();  
		   if (x == -1) {  
		     return -1;  
		   }  
		 } while (Character.isWhitespace((char)x));
		 charCount++;  
		  
		 // The '=' sign is just padding  
		 if (x == '=') {  
		   return -1;  // effective end of stream  
		 }  
		  
		 // Convert from raw form to 6-bit form  
		 x = ints[x];  
		  
		 // Calculate which character we're decoding now  
		 int mode = (charCount - 1) % 4;  
		  
		 // First char save all six bits, go for another  
		 if (mode == 0) {  
		   carryOver = x & 63;  
		   return read();  
		 }  
		 // Second char use previous six bits and first two new bits,  
		 // save last four bits  
		 else if (mode == 1) {  
		   int decoded = ((carryOver << 2) + (x >> 4)) & 255;  
		   carryOver = x & 15;  
		   return decoded;  
		 }  
		 // Third char use previous four bits and first four new bits,  
		 // save last two bits  
		 else if (mode == 2) {  
		   int decoded = ((carryOver << 4) + (x >> 2)) & 255;  
		   carryOver = x & 3;  
		   return decoded;  
		 }  
		 // Fourth char use previous two bits and all six new bits  
		 else if (mode == 3) {  
		   int decoded = ((carryOver << 6) + x) & 255;  
		   return decoded;  
		 }  
		 return -1;  // can't actually reach this line  
		}  
		  
		/*** 
		* Reads decoded data into an array of bytes and returns the actual  
		* number of bytes read, or -1 if end of stream was reached. 
		* 
		* @param buf the buffer into which the data is read 
		* @param off the start offset of the data 
		* @param len the maximum number of bytes to read 
		* @return  the actual number of bytes read, or -1 if the end of the 
		*      input stream is reached 
		* @exception IOException if an I/O error occurs
		*/  
		public int read(byte[] buf, int off, int len) throws IOException {
		 if (buf.length < (len + off - 1)) {  
		   throw new IOException("The input buffer is too small: " + len +
		    " bytes requested starting at offset " + off + " while the buffer " +  
		    " is only " + buf.length + " bytes long.");  
		 }  
		  
		 // This could of course be optimized  
		 int i;  
		 for (i = 0; i < len; i++) {  
		   int x = read();  
		   if (x == -1 && i == 0) {  // an immediate -1 returns -1  
		     return -1;  
		   }  
		   else if (x == -1) {       // a later -1 returns the chars read so far  
		     break;  
		   }  
		   buf[off + i] = (byte) x;  
		 }  
		 return i;  
		}  
		  
		/*** 
		* Returns the decoded form of the given encoded string, as a String. 
		* Note that not all binary data can be represented as a String, so this 
		* method should only be used for encoded String data.  Use decodeToBytes() 
		* otherwise. 
		* 
		* @param encoded the string to decode 
		* @return the decoded form of the encoded string 
		*/  
		public static String decode(String encoded) {
		 return new String(decodeToBytes(encoded));
		}  
		  
		/*** 
		* Returns the decoded form of the given encoded string, as bytes. 
		* 
		* @param encoded the string to decode 
		* @return the decoded form of the encoded string 
		*/  
		public static byte[] decodeToBytes(String encoded) {
		 byte[] bytes = null;  
		 try {  
		   bytes = encoded.getBytes("UTF-8");  
		 }  
		 catch (UnsupportedEncodingException ignored) { }
		  
		 Base64Decoder in = new Base64Decoder(  
		                    new ByteArrayInputStream(bytes));
		   
		 ByteArrayOutputStream out =
		   new ByteArrayOutputStream((int) (bytes.length * 0.67));
		  
		 try {  
		   byte[] buf = new byte[4 * 1024];  // 4K buffer  
		   int bytesRead;  
		   while ((bytesRead = in.read(buf)) != -1) {  
		     out.write(buf, 0, bytesRead);  
		   }  
		   out.close();  
		  
		   return out.toByteArray();  
		 }  
		 catch (IOException ignored) { return null; }
		}  
		  
		public static void main(String[] args) throws Exception {
		 if (args.length != 1) {  
		   System.err.println("Usage: java Base64Decoder fileToDecode");
		   return;  
		 }  
		  
		 Base64Decoder decoder = null;  
		 try {  
		   decoder = new Base64Decoder(  
		             new BufferedInputStream(
		             new FileInputStream(args[0])));
		   byte[] buf = new byte[4 * 1024];  // 4K buffer  
		   int bytesRead;  
		   while ((bytesRead = decoder.read(buf)) != -1) {  
		     System.out.write(buf, 0, bytesRead);
		   }  
		 }  
		 finally {  
		   if (decoder != null) decoder.close();  
		 }  
		}  
}
